add PolySynth.setType()

src/polysynth.js

@@ -210,6 +210,29 @@ class PolySynth {
     });
   }
 
+  /**
+   *  Set type to 'sine', 'triangle', 'sawtooth' or 'square'.
+   *  If the current synthVoice is not MonoSynth, it
+   *  replaces the current voice with MonoSynth.
+   *  @method  setType
+   *  @for p5.PolySynth
+   *  @param {String} type 'sine', 'triangle', 'sawtooth' or 'square'.
+   */
+  setType(type) {
+    if (!(this.audiovoices[0] instanceof p5.MonoSynth)) {
+      console.warn(
+        '`PolySynth.setType()` replaces the synthVoice with `MonoSynth`'
+      );
+      this.AudioVoice = p5.MonoSynth;
+      this.audiovoices = [];
+      this._allocateVoices();
+    }
+
+    this.audiovoices.forEach((voice) => {
+      voice.setType(type);
+    });
+  }
+
   /**
    *  Trigger the Attack, and Decay portion of a MonoSynth.
    *  Similar to holding down a key on a piano, but it will

test/tests/p5.PolySynth.js

@@ -57,6 +57,14 @@ describe('p5.PolySynth', function () {
         expect(monoSynth.env).to.have.property('control');
       }
     });
+    it('can change synthType', function () {
+      let polySynth = new p5.PolySynth(p5.MonoSynth, 6);
+      polySynth.setType('square');
+      for (let i = 0; i < 6; i++) {
+        const monoSynth = polySynth.audiovoices[i];
+        expect(monoSynth.getType()).to.equal('square');
+      }
+    });
 
     it('can trigger a note attack at the present moment with only one argument', function (done) {
       let polySynth = new p5.PolySynth(p5.MonoSynth, 3);